Not Applicable
Not Applicable.
This invention relates generally to docking systems and more particularly to a system for automatic docking of ships.
As is known in the art, conventional ships can have a primary propulsion system of two types. First, one or two propellers can be angularly fixed in a position parallel with the keel of the ship and a rudder can be associated with each of the propellers. Alternatively, one or two propellers may be angularly movable with regard to the keel of the ship and there may be no rudders. The term xe2x80x98secondary propulsion systemxe2x80x99 is used herein to describe any other propulsion system on the ship. Secondary propulsion systems are known to one of ordinary skill in the art to provide manual control of thrust at angles to the keel of the ship for tight maneuvers. For example, bow and stern thrusters are known in the art.
As is also known, a ship may have various forms of marine navigational equipment. Exemplary marine navigational systems include global positioning systems (GPS), magnetic compasses, gyro-compasses, radar systems, wind speed indicator systems, water current sensor systems, and marine speed logs.
The radar antenna of a conventional marine radar system is mounted high on the ship to allow the radar system to display objects at the greatest possible range from the ship. As is known in the art, a conventional marine radar system emits a pulsed beam of radar energy from the radar antenna and receives echoes by the radar antenna as the radar energy reflects off of objects in the path of the radar beam. The time delay between the transmitted pulse and the returned echo is used by the radar system to predict the range to a reflecting object. Typically, the radar beam is mechanically turned or xe2x80x9csweptxe2x80x9d in the azimuthal direction and the azimuthal steering of the beam is used to predict the azimuthal angle to the object. The conventional radar beam is swept azimuthally by mechanically rotating the radar antenna.
The beam width of a conventional marine radar is relatively narrow in azimuth, approximately 5 degrees, and relatively wide in elevation, approximately twenty five degrees, so as to form a vertically oriented fan shape. As with any projected energy, the fan shaped beam spreads spherically from the antenna, causing the fan shaped beam to have an outer xe2x80x98frontxe2x80x99 edge that is curved as if to lie on a sphere that has the radar antenna at its origin.
The fan shaped azimuthally rotated beam provides sufficient range prediction accuracy for objects that are relatively far from the radar antenna. Due in part to the curved wavefront of the fan shaped beam, the conventional marine radar system range prediction accuracy is greatest at long ranges and degrades at close-in distances. Essentially, for relatively short ranges, the conventional marine radar cannot distinguish range difference between a farther tall object and a nearer low object. Both the farther tall object and the short nearer object can produce echoes with the same time delay. Thus, the conventional radar beam is not well suited for close-in docking operations. Conventional marine radars have a minimum display range that is typically hundreds of feet and display resolutions of tens of feet. For ship docking, range accuracies and resolutions of less than plus or minus 1 foot would be desirable at ship to dock ranges within 25 feet.
As mentioned above, on some ships, the primary propulsion system and associated propeller are fixed to one axis along the keel, and the directional control is by way of a moveable rudder. In some cases there may be two propellers and two rudders. Regardless, directional control by way of the rudder is greatest when the ship is progressing rapidly through the water. Control by the rudder is developed by flow past the rudder and such flow becomes minimal when the speed of the ship through the water is low.
When docking, the speed of the ship is low and thus the directional control by the rudder is reduced. However, control by the rudder does not become zero at zero ship speed because the rudder is positioned to be in the flow of water created by the propeller.
For other primary propulsion systems, directional control is provided by a change of axial direction of the propeller. For example, an outboard motor is turned to provide propeller thrust at an angle to the keel that results in the desired ship direction. For these ships, directional control is somewhat maintained at low speed.
Both types of primary propulsion systems are conventionally mounted near the rear of the ship. Steering from points near the rear of the ship does not allow effective control of the ship in a direction perpendicular to the keel of the ship, the direction most advantageous for parallel docking. Thrust at an angle to the keel of the ship from a point or points near the rear substantially acts to rotate the ship. Control for docking, for example in the direction perpendicular to the keel, can only be approximated with the primary propulsion system by combinations of forward propulsions and reverse propulsions at angles off the keel axis. Each such fore or aft thrust produces a rotation of the ship, in alternating rotational directions. The control while docking is complex and ship pilots must have substantial experience to perform a docking using such a technique.
On some other ships, secondary propulsion systems have been used. Bow and stern thrusters are sometimes provided to yield more precise maneuvering of the ship. The secondary propulsion systems are often positioned to have thrust at or near to a direction which is perpendicular to the keel of the ship so as to provide thrust sideward to the long axis of the ship, a direction advantageous to docking.
Like the primary propulsion systems, during docking, the secondary propulsion systems known in the art are manually controlled by the operator of the ship. Like manual control of the primary propulsion system during docking, manual control of the secondary propulsion systems is also relatively difficult due in part to water current and wind that act to move the ship in any direction relative to the direction of docking. Control of the primary propulsion system in combination with the secondary system is often needed to control the ship during docking in two dimensions, along the keel and perpendicular to the keel.
It is well known in the art that docking error can result in damage to the ship and/or to the dock. As conditions become increasingly windy or where the water current is high, the likelihood of damage is greatest. The docking maneuver requires complex manual fore and aft thrust from the primary propulsion system or complex thrust control of the secondary propulsion system.
Conventional docking systems only provide display information to the operator of the ship. The information is provided to an operator of the ship so that the operator can manually control the ship""s primary and/or secondary propulsion system to bring the ship to dock.
It would, therefore, be desirable to provide a system that automatically controls the vessel propulsion system and aids in docking a ship. It would also be desirable to provide a system which conveys accurate range data to an operator of a ship when the ship is in close proximity (e.g. 25 feet or less) to dock or a docking structure. It would be further desirable to provide a system which displays docking data to an operator of a ship.
In accordance with the present invention, a system for automatically docking a ship includes a secondary propulsion system coupled to the ship for automatic steering of the ship, a docking processor coupled to the secondary propulsion system to control thrust provided by the secondary propulsion system and one or more radar systems coupled to provide navigational information to the docking processor wherein the docking processor uses the navigational information provided by the radar systems to control the thrust.
With this particular arrangement, the auto-docking system of the present invention provides automatic control of a secondary propulsion system to more accurately and safely dock a ship. The auto-docking system utilizes conically shaped radar beams narrow in two dimensions that are electronically steered. The conical beams provide accurate close-in radar range data. With these characteristics, the auto-docking system of the present invention can dock a ship in difficult conditions, with wind and water current, without manual intervention. The likelihood of manual docking error and resulting damage are minimized.